Indeks
Just like your car, a boat's engine produces heat. On your car this heat is removed by the airflow circulating around the engine and the radiator. On a boat the principle is very similar with a few minor differences.
There are two general types of cooling systems found on most boats: open cooling or closed cooling systems. Both systems use the water that the boat is sitting in for cooling purposes, the difference lies in where that water flows and what components are cooled. On both systems the water flow is usually the same up to the oil cooler with some minor differences between inboard boats versus inboard/outboard boats.
--Open Cooling System (Seawater or Raw Water Cooled)--
If the engine is cold, the thermostat assembly routes the water to the exhaust risers where it is passed overboard through the exhaust. The water contained in the engine remains in essentially a closed circuit moving from the engine cooling passages to the thermostat assembly to the engine circulating pump then back to the engine cooling passages. This closed circulation allows for a quick warmup.
As the temperature of the water passing through the thermostat assembly increases, the thermostat begins to open allowing the hot water to be sent to the exhaust manifolds where it is discharged overboard. The thermostat assembly also allows the incoming cold water to mix with the hot engine discharge water, this cooler water is now routed to the engine circulating pump then to the engines cooling passages.
This system uses the thermostat to maintain the engine within operating parameters. As the water temperature fluctuates the amount of cold water added to the engines circulating system is controlled by adjusting the discharge path of the water. If the engine is too hot, water is allowed to discharge via the exhaust manifolds and more cold water is introduced into the engines circulating system. If the temperature is too cold, the cold water bypasses the engines circulating system and is discharged overboard through the exhaust risers. Click the Thermostat Closed button to see the differences in water flow.
--Closed Cooling System (Freshwater Cooled)--
The closed cooling system is composed of two separate subsystems. A closed cooling system (freshwater system) and seawater system. The system operates similar to the cooling systems on automobiles. However, instead of a radiator boats utilize a heat exchanger.
On a car the engines hot water is pumped through the fins of the radiator while cool air passes over the fins absorbing the heat and cooling the water. On a boat the cool water (seawater) is pumped through a flow tube inside the heat exchanger removing heat while the engines hot water (freshwater) circulates around it the tube.
Seawater (Raw Water) Subsystem
Cold seawater is pumped into one end of the heat exchanger where it circulates around the flow tube before exiting out the other end of the heat exchanger. The seawater then exits the discharge end of the heat exchanger and is routed to the exhaust risers where it is discharged overboard.
Closed Cooling (Freshwater) Subsystem
Freshwater is routed from the engine to the thermostat assembly. From there the freshwater goes to the exhaust manifolds cooling passages then to the heat exchanger. The freshwater passes through the flow tube transferring its heat to the seawater. When the freshwater exits the heat exchanger it is routed to the engine circulating pump and pumped through the engine's cooling passages to return to the thermostat assembly.
This system behaves somewhat differently in how it maintains the operating temperature within the optimum range. The thermostat opens allowing a higher volume of water flow through the heat exchanger as the temperature increases, the reverse is true if the temperature is too low.
There are two general types of cooling systems found on most boats: open cooling or closed cooling systems. Both systems use the water that the boat is sitting in for cooling purposes, the difference lies in where that water flows and what components are cooled. On both systems the water flow is usually the same up to the oil cooler with some minor differences between inboard boats versus inboard/outboard boats.
--Open Cooling System (Seawater or Raw Water Cooled)--
If the engine is cold, the thermostat assembly routes the water to the exhaust risers where it is passed overboard through the exhaust. The water contained in the engine remains in essentially a closed circuit moving from the engine cooling passages to the thermostat assembly to the engine circulating pump then back to the engine cooling passages. This closed circulation allows for a quick warmup.
As the temperature of the water passing through the thermostat assembly increases, the thermostat begins to open allowing the hot water to be sent to the exhaust manifolds where it is discharged overboard. The thermostat assembly also allows the incoming cold water to mix with the hot engine discharge water, this cooler water is now routed to the engine circulating pump then to the engines cooling passages.
This system uses the thermostat to maintain the engine within operating parameters. As the water temperature fluctuates the amount of cold water added to the engines circulating system is controlled by adjusting the discharge path of the water. If the engine is too hot, water is allowed to discharge via the exhaust manifolds and more cold water is introduced into the engines circulating system. If the temperature is too cold, the cold water bypasses the engines circulating system and is discharged overboard through the exhaust risers. Click the Thermostat Closed button to see the differences in water flow.
--Closed Cooling System (Freshwater Cooled)--
The closed cooling system is composed of two separate subsystems. A closed cooling system (freshwater system) and seawater system. The system operates similar to the cooling systems on automobiles. However, instead of a radiator boats utilize a heat exchanger.
On a car the engines hot water is pumped through the fins of the radiator while cool air passes over the fins absorbing the heat and cooling the water. On a boat the cool water (seawater) is pumped through a flow tube inside the heat exchanger removing heat while the engines hot water (freshwater) circulates around it the tube.
Seawater (Raw Water) Subsystem
Cold seawater is pumped into one end of the heat exchanger where it circulates around the flow tube before exiting out the other end of the heat exchanger. The seawater then exits the discharge end of the heat exchanger and is routed to the exhaust risers where it is discharged overboard.
Closed Cooling (Freshwater) Subsystem
Freshwater is routed from the engine to the thermostat assembly. From there the freshwater goes to the exhaust manifolds cooling passages then to the heat exchanger. The freshwater passes through the flow tube transferring its heat to the seawater. When the freshwater exits the heat exchanger it is routed to the engine circulating pump and pumped through the engine's cooling passages to return to the thermostat assembly.
This system behaves somewhat differently in how it maintains the operating temperature within the optimum range. The thermostat opens allowing a higher volume of water flow through the heat exchanger as the temperature increases, the reverse is true if the temperature is too low.
